Add a whole Youtube playlist to watch later - so you can clone the list easily

clone-youtube-playlist.js

// this script copies a youtube playlist to the "watch later" list, so you can easily clone the
// list by creating a new one off the watch later list. You must run this on a playlist overview
// page like http://www.youtube.com/playlist?list=xxxxxxxxx

// this script is meant to be converted into a bookmarklet, using something like http://mrcoles.com/bookmarklet/
// after conversion, it becomes this:
// javascript:(function()%7Bvar%20buttons%20%3D%20document.querySelectorAll(%22button.addto-watch-later-button%22)%3Bvar%20videos%20%3D%20document.querySelectorAll(%22.playlist-video-item%22)%3Bif%20(videos.length%20!%3D%20buttons.length)%20%7Balert(%22Some%20videos%20are%20already%20in%20watch%20later!%20Found%20%22%20%2B%20videos.length%20%2B%20%22%20videos%20but%20%22%20%2B%20buttons.length%20%2B%20%22%20buttons.%20Abort%20now.%22)%3B%7D%20else%20%7Bif%20(confirm(%22Add%20%22%20%2B%20buttons.length%20%2B%20%22%20videos%3F%22))%20%7Bvar%20dialog%20%3D%20document.createElement(%22h1%22)%3Bdialog.innerHTML%20%3D%20%22%3Cdiv%20style%3D'color%3Ared%3Bposition%3A%20fixed%3Btop%3A%200%3Bfont-size%3A%20100px%3Bmargin%3A%20120px%20auto%3Bbackground%3Awhitesmoke%3Bz-index%3A%201000%3Bwidth%3A%20100%25%3Btext-align%3A%20center%3B'%3EWorking...%3C%2Fdiv%3E%22%3Bdocument.getElementById(%22body-container%22).appendChild(dialog)%3Bfor%20(var%20i%20%3D%20buttons.length%20-%201%3B%20i%20%3E%3D%200%3B%20i%20--)%20%7BsetTimeout(function(j)%7Bbuttons%5Bj%5D.click()%3B%20console.log(j%20%2B%20'%20left')%3B%20if%20(j%20%3D%3D%200)%20alert(%22all%20done%22)%20%7C%7C%20dialog.parentElement.removeChild(dialog)%7D%2C2000*(buttons.length-i-1)%2C%20i)%3B%7D%7D%7D%7D)()

var buttons = document.querySelectorAll("button.addto-watch-later-button");
var videos = document.querySelectorAll(".playlist-video-item");
if (videos.length != buttons.length) {
    alert("Some videos are already in watch later! Found " + videos.length + " videos but " + buttons.length + " buttons. Abort now.");
} else {
    if (confirm("Add " + buttons.length + " videos?")) {
        var dialog = document.createElement("h1");
        dialog.innerHTML = "<div style='color:red;position: fixed;top: 0;font-size: 100px;margin: 120px auto;background:whitesmoke;z-index: 1000;width: 100%;text-align: center;'>Working...</div>";
        document.getElementById("body-container").appendChild(dialog);
        for (var i = buttons.length - 1; i >= 0; i --) {
            setTimeout(function(j){buttons[j].click(); console.log(j + ' left'); if (j == 0) alert("all done") || dialog.parentElement.removeChild(dialog)},
                       2000*(buttons.length-i-1), i);
        }
    }
}

Works with minor change (.playlist-video-item to .pl-video)

tried loatroll's tip. 'add 0 videos?' every time